The purpose of the research is to gain an understanding of the mechanism of self-assembly of tubulin and the control of microtubule formation and depolymerization. In these studies we are examining the polymorphism of tubulin self-assembly by determining the effects of a number of variables on the protofilament number of formed microtubules and on the formation of complex ribbons and sheets of protofilaments. We are also investigating the types of intermediates which are present during self-assembly of 6S tubulin. The roles of sulfhydryl and disulfide bonds in tubulin are being examined. These will be modified specifically with agents such as fluorodinitrobenzene, N-ethylmaleimide, dansyl chloride, dansylaziridine, and 2-mercaptoethanol. Effects on the physical structure of tubulin by these agents will be determined by difference spectroscopy, fluorimetric and circular dichroism spectroscopy studies. The function of the tightly bound metal ion is also being examined. The effects of exchanging bound Mg with Mn, Zn, and Co on the physical structure of tubulin and the self-assembly reaction will be investigated.